The present invention relates to a method and an apparatus or plant for carrying out the degradation of organic products, by-products and scraps or waste from human, animal and/or vegetable origin.
More specifically the subject matter of the invention is a process and a device for performing a continuous methanizing of solid and/or liquid organic compounds.
Organic materials from various sources such as human, animal or vegetable origin may lead through successive or simultaneous microbiological degradations in an anaerobic medium to gaseous compounds the most important of which are methane and carbon dioxide.
The nature and composition of these organic products are very variable and they consist of more or less polymerized and imbricate elements. These organic products would mostly form a solid substrate whether fibrous or not with a high content of dry matter. This is in particular the case of town and agricultural refuse, garbage or litter for instance. Such products may however also be liquid with small contents of dry matter such for instance as the sludges from purification plants or stations, liquid manures, milk serum.
The major part of such substrates consists of ternary compounds such as sugars, starches, hemicelluloses, celluloses and lignins but quartenary substances such as protides and peptides may also be associated therewith.
The agents participating in such degradations are generally coming from animal, plant and telluric habitats. Numerous species or kinds have been found out. They are evolving within mediums with very variable pH and reduction-oxidation potential with ranges differing with the psychrophilous mesophilous or thermophilous kinds.
In a simplified manner the degradation of an organic matter and in particular of an insoluble organic matter in an anaerobic medium would proceed according to three steps:
a hydrolysis step during which the enzymes would convert the insoluble compounds into soluble substances;
an acidogenous step during which dissolved organic matters are converted into compounds such as fatty acid, alcohol or others. During that acidogenous step there is an acetogenous step during which is generated acetic acid which is one of the compounds which are essential for the formation of methane during the following last step:
a methanogenous step during which methane and carbon dioxide are produced.
Fermentation processes are already known which consist in using digestion tanks, vats or like vessels operating continuously or discontinuously (batch production). The batch-wise or discontinuously operating tanks are used especially with organic products or solid and heterogeneous substrates and are neither convenient nor industrially profitable. The continuously operating digestion tanks are almost essentially used with liquid effluents with a small content of dry matter. In such devices indeed, the treatment of a solid substrate whether heterogeneous or not involves many difficulties in particular in connection with the circulation and homogenization of the substrate within the tank thereby resulting in bad operating conditions and strongly disturbing or interfering with the process of degradation of organic matter. The efficiencies or yields of such plants are relatively low. To provide for a methanizing under suitable conditions, it was therefore necessary to use a liquid substrate or a substrate greatly diluted through addition of water. This amount of water associated with the substrate to be processed would result in the occurrence of polluting liquid refuse and the use of bulky tanks.
From the French patent specification publication No. 2,305,113 is for instance known an apparatus for the digestion of organic matters wherein the material to be processed after having been damped or moistened is fed into a cylindrical compartment wherein it undergoes an aerobic fermentation under pressure and is then driven or pushed by a ramming piston through a bent syphon into a small anaerobic fermentation compartment and thereafter into a large compartment. Within the bend or elbow of the syphon forks would prevent the material from flowing back. According to said patent specification, there is also provided an extraction shaft or well wherein the fermented matter is carried along by a claw.